A “reverse-flow core gas turbine engine” refers to a gas turbine engine wherein flow of air through the engine is reversed after passing through a low pressure compressor. Reverse manifolding redirects rearward flowing air from the low pressure compressor to flow in a forward direction through a core of the engine. Exhaust ducting then re-directs an exhaust gas stream from the core to an engine exhaust. A reverse-flow core gas turbine engine is described in detail U.S. Pat. No. 8,176,725 that issued to Norris et al. on May 15, 2012, which patent is owned by the owner of all rights in the present application and which patent is also hereby incorporated herein by reference thereto.
Norris et al. resolves a problem associated with a low pressure shaft that connects a low pressure compressor and low pressure turbine being co-axial with a high pressure shaft that connects a high pressure turbine with a high pressure compressor in conventional gas turbine engines. Because the two shafts are co-axial, at least one of them must have a greater diameter and be made of stronger materials than would be required if the shaft could be shorter. By reversing the flow of the inlet air passing through the engine, a low spool may have a first or low pressure shaft connecting a low pressure compressor and a low pressure turbine, while a separate, non-coaxial, second or high pressure shaft connects a high pressure turbine with a high pressure compressor of a high spool.
In Norris et al., the low pressure compressor, low pressure shaft and the low pressure turbine are referred to as a “low spool”. Similarly, the high pressure compressor, the high pressure turbine, a combustor between the high pressure compressor and high pressure turbine, and a high pressure shaft are referred to as a “high spool”. More specifically, Norris et al. discloses that the low spool includes a rearward-flow low pressure compressor and a forward-flow low pressure turbine disposed aft of the rearward-flow low pressure compressor. The low pressure shaft is secured between the low pressure turbine and the low pressure compressor. The high spool is disposed aft the low spool and includes a forward-flow high pressure turbine disposed aft of the forward flow of the low pressure turbine, a combustor disposed aft of the forward-flow high pressure turbine, a forward-flow high pressure compressor disposed aft of the combustor. The high pressure shaft is secured between the high pressure turbine and the high pressure compressor. Because the two shafts are separate, the low pressure shaft may be shorter and narrower, as described above. Additionally, the high pressure shaft does not need to be wide enough accommodate the low pressure shaft, and therefore bath shafts and hence both spools and their associated rotors and discs comprising the turbine and compressors may be reduced in size and weight, thereby reducing costs associated with manufacturing parts from high strength engine alloys. An exemplary reverse-flow core gas turbine engine is the Honeywell ATF3 which is a 3-spool turbofan engine that has been in production for over twenty years with more than 200 engines in service. The ATF3 engine applications include the DASSAULT “Falcon 20G” brand aircraft used by the U.S. Coast Guard and the French Navy, and on the “Falcon 200” brand business jet.
It has become increasingly common to combine gas turbine engines with pulse detonation engines (“PDEs”). It is generally known that such engines operate by producing a series of pulsed detonations within one or more firing tubes of the engine. An oxidant such as atmospheric air and fuel are directed into an inlet of the firing tube and then combusted within the tube. This results in a dramatic pressure rise as a pressure wave of combusted oxidant and fuel moves along the firing tube increasing in velocity to produce a detonation wave that results in very substantial thrust as an exhaust stream passes out of an outlet of the firing tube.
It is also known that PDEs are combined with traditional gas turbine engines, wherein the exhaust stream from the pulse detonation engine (“PDE”) is directed to flow into the turbine to drive the turbine. In such turbine hybrid PDEs, it is common that the turbine typically drives a compressor to force air into one or more of the firing tubes within the PDE. For example, U.S. Pat. No. 6,666,018 that issued on Dec. 23, 2003, to Butler et al. discloses a “combined cycle pulse detonation turbine engine” wherein a pulse detonation core is utilized to replace either a combustor of a core engine, or to replace a high pressure turbine, compressor and combustor of the engine.
Such combined as turbine and pulse detonation engines have not gained wide-spread usage because of many problems associated with extraordinary heat and vibration generated by operating PDEs as well as a substantial axial length of firing tubes of PDEs.
Therefore, there is a need for a gas turbine engine combined with a PDE that enhances efficiencies of the resulting engine.